1. Field of the Invention
The invention relates to a charging device for an electromotive vehicle and, more particularly, to charging control for charging an electrical storage device, equipped for an electromotive vehicle, by a power supply outside the vehicle.
2. Description of Related Art
An electric vehicle, a hybrid vehicle, a fuel cell vehicle, and the like, are known as electromotive vehicles that are configured to be able to generate vehicle driving force using electric power from an in-vehicle electrical storage device, typically, a secondary battery. There has been suggested an electromotive vehicle that is configured to charge an in-vehicle electrical storage device by a power supply outside the vehicle (hereinafter, also simply referred to as “external power supply”). Hereinafter, charging the electrical storage device by the external power supply is also simply referred to as “external charging”.
Japanese Patent Application Publication No. 2007-318970 (JP-A-2007-318970) describes that a charging device that converts electric power, supplied from an external power supply, to electric power for charging an electrical storage device is formed of two alternating-current motors equipped for a hybrid vehicle and inverters and step-up converter for driving these alternating-current motors. The charging device described in JP-A-2007-318970 is configured to receive electric power from the external power supply via respective neutral points of the two alternating-current motors.
In addition, Japanese Patent Application Publication No. 2009-33785 (JP-A-2009-33785) describes charging control in a power supply system of an electromotive vehicle, in which a plurality of pairs of electrical storage device and converter are arranged in parallel with each other. Specifically, JP-A-2009-33785 describes control for charging each electrical storage device by keeping an upper arm element of a corresponding step-up chopper DC-DC converter circuit (converter) in an on state.
In the charging device described in JP-A-2007-318970, when electric power supplied from the external power supply is converted to electric power for charging the electrical storage device, there is a limit for increasing the charging efficiency because of a power loss in switching elements resulting from DC-DC conversion operation or an iron loss and copper loss of a smoothing inductor.
JP-A-2009-33785 describes that the electrical storage device is charged with the increased efficiency of each chopper DC-DC converter circuit in such a manner that the upper arm element of any one of the DC-DC converter circuits is kept in an on state, but JP-A-2009-33785 does not specifically describe under what condition such charging control should be applied. However, depending on the state of external charging, when the upper arm element of any one of the DC-DC converter circuits is kept in an on state, there may occur a case where efficiency in elements other than the DC-DC converter circuit decreases or a case where excessive current occurs.